Method of treating waste pickle liquor.



AJR-HOFFMAN & w. M. PARKIN. METHOD 0F T REATNG WASTE PI'CKLE LQUR.

APPLICATION FILED APR. 8. NIMH.

Patented June 11, 1918.

` @SER vic..

ALF PABKIN, 0F PITTSWEG-H, PEN'NSYL- ImTHOD 0F TREATING 'WASTE PICKLELIQUOR.

application mea april a, 191e, serial No. 89,932.

burgh, in the county of Allegheny and State of Pennsylvania, haveinvented new and useful Improvements in Method 'of Treat- 4 ing WastePickle Liquor, of which the following is a specification.

This invention relates` to a process of treating waste pickle liquorproduced as a by product in pickling 1ron articles in anacid solutioncontaining sulfuric acid.

The solution of sulfuric acid and water used in cleaning of picklingmetals at industrial plants is usually strengthened from time to time bythe addltion of acid and its use is continued until it shows a densityof about 22 Bei, when it is generally discarded. To continue thesolution inl use longer would so increase the density of the solutionthat the crystals of ferrous sulfate (FeSO47H2O) might` form on thesurface of' the metal which is being cleaned.

Our aim is to use the solution as long as is practical, at or near theboiling point, so that the subsequent evaporation of excess I water (inproducing ferrous sulfate crystals or copperas) will be small.

The accompanying drawings show, somewhat diagrammatically, an apparatussuitable for use in carrying out our process. In

`said drawings lFigure 1 is an elevation, partly in section of such anapparatus, and Fig. '2 is a plan view thereof. l

In carrying out our-invention the spent or waste pickle liquor ispermitted to flow or is pumped) from the pickling tanks, which may besituated at various points in the mill and usually `connected with themill sewer) to a settling tank 1, conveniently located but preferabl4underground* and covered so that it wil notJ take up needed andvaluable yard room, and also so that it will preserve the heat in orderto economize fuel in the subsequent evaporation of the liquor. Insolublematter settles in this tank and for this reason a-sewer connection isprovided for the purpose of cleaning it at intervals. The free acidwhich in practice is usuall present to an extent of about 100 poun s toevery 750 gallons is not neutralized. 2 is a relatively small sump tankinto which the clear liquor blower thereto.

' Specification of Letters Patent. .Pmhud Jun@ 111, 39h86 RenewedNovember 10, 19 17l. Serial No. 201,899.

.flows from the tankl or tanks 1. Adjacent to the sump tank is aconcentrator 3,' which may consist of a stack or tower containing arefractory filling material as for example some suitable silicious rockor other inert filler over which the waste pickleA may be caused toflow. A furnace 4 is shown as connected to the stack and this furnacemay be of any suitable form for example an ordinary rotaV type now foundupon the market. The ot vgases rising through the interstices of thefiller 3 causes evaporation of the surplus water in the waste pickleliquor as it flows over the filler. Below thel tion containing ferroussulfate, ferric sulfate and sulfuric acid Hows, into the crystallizingtanks 6, where it is permitted to cool and deposit ferrous sulfatecrystals Jon wooden rods or racks suspended in these tanks. If desiredevaporation may be ac-` celerated in the concentrator by attaching a Themotherliquor that is the liquor after crystallization has taken place,still contains some ferrous and ferrie sulfates, and considerable freesulfuric acid, is then returned to the pickling tanks, where it may bemixed with `water and acid andreused in cleaning metals;

The recovered copperas is a commercial article, -but it is the intentionto use it in a later stage of this process. Any ferric sulfate presentis permitted to remain in the mother liquor as it is of advantage in thepickling operation.

`After the ferrous sulfate crystals are drained, they are crushed topowder and Aallowed to oxidize in moist air, although thisl action maybe-accelerated by blowing air, either hot or cold, through the mass. Thereaction is as follows:

areso4+o+H2o=re2(sogarqornz.

llOO

Lit

. sderably higher and the- We have found that if this basic ferriersulfate be heated: in contact with water or water vapor, it will breakup into sulfuric acid and ferric hydrate. lAs the temperature increases(between 179` and 3389.0), sulfurie acidv and water distil from thematerial, leaving ferrie oxid. The chemical equations are approximatelyas follows; Fe- (SO .Fe(OI-I) |6H O: l

2 4 3 i 3- ltsosiaoH-t `Should there' not be suilicientwater pres entthe ten'nperature required would be con- I decomposition equation wouldbe: amuse) .Moin j: A

posed into SO2 and O.) I

An kind of fuel may be used, forex- `.amIple oil, coke, natural orproducer gas or P11 verized coal, but care should be taken that therewill be as little smoke produced as is possible.

The vapors and hot gases given off during this heating step are thenpassed from the furnacel to and through the filled tower r3, throughwhich thel cleaned liquoris owing, the acid there being absorbed, while.

. water is evaporated from the liquor. In practising our invention, wehave recovered as much as 95%l of the total SOalcontent oflthe wastepickle liquor, both the VH10504 vapor "and the lSO8 fumes being.absorbed in the tower 3.

Should the crystals not be completely changed to. basic ferrie sulfatebefore calcination the reaction would partly be the acid radicalV in thecrystals would be lost.

Itis evident that vthe acid vapors can be. vhandled differently than bythe mode above y described and strong acid produced instead the basicferrie sulfate -to the furnace, but- .for convenience of illustration wehave or as rouge.

of absorbing the acid .vapors injthe waste pickle liquor;

Any means may be einployed'for feeding shown a hopper 7 for thispurpose. The ferrie oxid discharged from theflower end ofthe kiln issuitable for use as pigment Ifdesired a pyrometer may be used on v orlin the .kiln to indicate the temperature 'and the kiln temperature willbe regulated accordin to the pyrometer readings.;

It will be noted that the temperatures necessary in the heating step ismaterially lower than the temperatures heretofore used in thecalcination of-ferrous sulfate. resulting pigment is also of a muchbetter i k(Part of.,l.lie SO3 would also be decom i fur, ybut vthis 3,evaporatin The quality than that produced by the calcination of ferroussul ate.

-By calcining the basic ferrie sulfate, and

concentrating the waste pickle liquor by the waste heat of saidoperation, it will be seen that the mother liquor-will be suitable foi"pickling, as very little offthe acid will condenser 3..

Theoretically one tn of sulfuric'acidf of 66 B., used to exhaustion incleaning iron' or steel would containsuiiicientferrous sulfate toproduce 1 520 lbs. 'of ferric oxid. In actual practice,- the acid ofthepickle liquor is not completely exhausted, so tha'taSmallerr nient asmall uantit of salt (NaCl)'may r be added to t e sul ate beforecalcination to aidinthe complete elimination. of sulaplies only whencalcination is used, z. e., w en heated to much hi her temperatures thanabove specified. ere the temperature of treatment is lowertlian required'toA decompose all the sulfate or basic sulfate, the product should'bebolted and washed with an alkaline solution to' eliminate traces ofsulfur.` a

Instead of concentratin the waste' pickle liquor by heat furnished y thefurnace 4 heat from a separate furnace may be use or there may-be aplurality of concentrators the surplus moisture from the waste piceliquor. The enriched waste pickle liquorfrom the concentrator may bethev tein- .be lost, the vaporizing point of thel acid `being muchhigher than that ofthe water .which is removed from itheliquor inthe'distributed .among several tanks or the mother liquor from several tanksmay be transferred to a storage tank where a more `uniforn1 liquor willresult which may be,

run into the pickling tanks as wanted.

Instead of oxidizing the copperas, or ferrous sulfate, there maybecertain conditions where it maybe referable to calcine the 'ferroussulfate, t ereb losing aboutl one half ofthe sulfate ra ical andrecovering ferric oxid, wasting the sulfur dioxid'or collecting it foruse in making soineother product, for example'calcium sulte.

Any suitable form of apparatus" may be invention.

What we claim is: 1. The method of treating sulfuric acid yemployed tocarry out ourinvention, thef details of parts herein' described beingonlyillustrative of one means for practising the waste pickle liquor forthe recovery of sul# furie acid and ferrie oxid, which vconsists inering the ferrous sulfate -in the furie Lacanau collecting the wastepickle liquor and removing extraneous ,matter therefrom, then recoveringthe ferrous sulfate in the form of crystals, pulverizing the crystalsand oxidizing the same, then subjecting the product to the action ofheat to drive olf sulfuric acid and water producing ferrie oxid andcollect.-l ing the ferrie oxid and sulfuric acid. v 2.*The method oftreating sulfuric acid waste pickle liquor for'the recovery of sulacidand ferrie oxid, which consists in collecting the waste pickle liquorand recovform of crystals, ing the product -of such treatment lwhileagitating the same, to a temperature'suirlcient to drive off the acidradical and water, producing ferrie oxid and 'collecting the sulfuricacid and -ferric oxid.

3. The method of treating sulfuric acid waste pickle liquorA which.conslsts in res movin imentation, concentrating the waste pickleliquor, crystallizing out ferrous sulfate, crushing and'l oxidizinthe'crystals thereby changingl ferrous s fate to ferrie sulfate,subjecting the ferrie sulfate to the action of heat sulicientto produceferrie oxidizing the ferrous sulfate, heat-4 from the solution insolublematter oxid, absorbing the vapors from the said heating operatlon inwaste pickle 1i uor and returning the acid mother, liquor om thecrystallization step to the metal pickling operation.

4. The herein described process of treating waste sulfuric acidpckleliquor, which comprises settling out a material proportion ofthe-insoluble impurities, and thereafter without neutralizat1on'-of thefree acid or reduction of the fel-'ric compounds therein,

, concentrating the relatively clear liquor by subjecting flowingcurrents 4thereof to theaction of a gas current containing acidformingvapors, crystallizing out a material quantity of the ferrous sulfatecontent, 0m`- dizing the ferrous sulfate and subjecting the oxidizedproduct to heat in the presence of steam, at a temperature between 179and 338 C..

In testimony whereof we ax our :signa-4 tures 1n presence of twowitnesses.

ADDISON F. HFFti t WILLIAM iii/minnaar an. Witnesses:

lB. l?. Hormom, S. S.

